Microelectronic devices contain millions of electrical circuit components supported by various types of substrates. The components include semiconductor silicon dies (chips). Electrical connections between these components and substrates are made between electrical terminals on the die and corresponding electrical terminals on the substrate. One method for making these connections uses a paste die attach adhesive to adhere the semiconductor die to the substrate and metal wires to bond the terminals on the die to terminals on the substrate.
In this die attach process, the die is contacted to the die attach adhesive with a sufficient degree of pressure and/or heat so that the adhesive spreads and completely covers the substrate under the die. It is desirable that the adhesive further forms a fillet, that is, a raised rim or ridge, at the periphery of the die.
Problems arise in the dispensing of die attach adhesives when thin dies are used and when dies are stacked. Conventional paste die attach materials are not suitable for these applications because the die attach material does not readily form a fillet at the desired boundary and can easily overflow into the crowded real estate of the semiconductor package and contaminate neighboring dies and electrical interconnects, or onto the top of the die, which will affect subsequent wire-bonding process. In addition, the right levels of adhesive flow and bonding are difficult to achieve without the application of pressure. When pressure is applied to thin dies, the dies can crack, or tilt, or warp.
It would be preferable to apply a die attach material that has the right rheology to automatically flow and fill the area to be adhered without, or with minimal, application of pressure and/or heat, and to form a fillet accurately and uniformly at the perimeter of the area without the adhesive spreading onto peripheral areas.